The present invention is directed to chemiluminescent reactions. Chemiluminescent reactions which occur between two chemicals or gases result in the emission of photons or light energy. In analytical instruments manufactured for monitoring gases, a common chemiluminescent devices titrate a reagent with a sample to form NO.sub.2 plus energy (in the form of a light photon) and oxygen.
Chemiluminescence, under the right conditions, is an extremely sensitive method in both qualitative and quantitative determinations. The reactions from chemiluminescent reactions can correlate the emissions of photons with each molecule of interest, and thus can qualitatively and quantitatively determine for the presence of the molecule of interest at very low levels. Commonly, a typical reagent is the gas phase of ozone (atomic oxygen). Unfortunately, the reaction is not very selective and compounds like sulphur dioxide, nitrogen oxides and unsaturated hydrocarbons may produce emissions which can interfere with proper detection.
Because of efforts to reduce atmospheric pollution, reliable methods are needed for monitoring the level of various individual criteria gases from both the ambient atmosphere and various effluent sources, such as vehicle exhausts and the like. The detection of the presence of pollutants in part-per-million (PPM) levels by the observation of chemiluminescent reaction is particularly attractive because the method can be adapted to be continuous since long-length observation is not required, as in absorption spectroscopy. Traditional chemiluminescent detectors typically comprise a properly sized chamber where two gases, a sample and a reagent, are mixed uniformly so that virtually all of the NO is converted to NO.sub.2. The resulting reaction produces a light photon which may be detected by a photo multiplier tube or solid state detector.
Such chambers are typically constructed with a window at one end so that a sensor, either a PMT (photo multiplier tube) or solid state detector, can register the level of light intensity resulting from the reaction (collision) of the gases.
While there are a number of chemiluminescent detectors, each share a number of common design considerations. First, the mixing of the two gases into the chamber must be turbulent so that the reaction is complete. The reaction must occur to close the window. It is assumed that the light distribution across the window is uniform, but it is usually a single spot.
The light generated from the reaction is diffuse in nature. The intensity of light decreases by a factor of the reciprocal of the distance from the excited molecules to the sensor squared. This principle is well known to those skilled in the art as the "Inverse Square Law". Because the chamber has a volume, the gain is dependent upon the design and typically is never fully optimized. To improve the chamber output, chambers are sometimes gold coated in order to improve their internal reflectance and thus the total light output. The response time of the analytical instrument is also effected by the volume of the chamber. The volume of the instrument should be kept low because the response time is generally important to users. Further, the materials used in constructing the chamber must be considered in the case where samples are corrosive so that the materials do not react with the sample or reaction by-product. The flow controls for the sample and reagent are external to the chamber.
The prior art is replete with examples of chemiluminescent detectors. None are directed to devices such as disclosed and claimed in the present invention. U.S. Pat. No. 4,555,491 discloses a reaction cell in which a quartz cell includes two quartz tubes which carry gas until they meet at a turbulence gap. An exit line permits the gases to be swept away for continuous monitoring. The device disclosed in this invention is typical of prior art devices in which a chemiluminescent reaction occurs at a single location or point on the detector.
U.S. Pat. No. 3,856,473 discloses a system in which optical chopping is utilized to modulate the luminescent signal into the A/C domain. The ozonator is energized periodically, e.g., in a pulsed mode.
U.S. Pat. No. 3,882,028 discloses apparatus adapted for measuring concentrations of constituents in a gas near ambient pressure by measuring the extent of chemiluminescent reaction which may occur in each of several small reaction chambers. In order to counteract the quenching effect associated with chemiluminescent reactions, and to promote more complete and rapid reactions in a reduced volume, each reaction chamber utilizes a concentric feed nozzle when an orifice is circumscribed by an opening for a second reactant such as ozone and in which the reactants are introduced at moderate pressure in intimate mixture into a relatively small reaction chamber.
U.S. Pat. No. 5,250,259 discloses a chemiluminescent detector which has an integral structure of the reaction unit and a detection unit. U.S. Pat. No. 3,963,928 discloses a signal processing means to demultiplex a light signal and to determine the relative concentration of constituents not directly observable by chemiluminescence or not distinguishable by observation.
U.S. Pat. No. 4,301,114 discloses a sieve trap which holds a number of packings. U.S. Pat. No. 4,765,961 similarly uses a system of traps instituting chemiluminescence reactions. Finally, U.S. Pat. No. 3,763,877 is directed to a fluid flow control system which maintains a constant fluid sample flow to a treating chamber.
Each of the prior art systems this facilitate chemiluminescent reactions by varying pressure or by eliminating noise or which create a reaction at a single location or point on the detector. While mass flow is a major issue, the control of flow has not heretofore been controlled in the detector. It would be desirable to provide a new design for a chemiluminescent detector constructed from micro-machine silicon and bonded to fused silica, quartz, glass, pyrex or any clear polymer. The surface of such a detector could comprise three major flow paths or conduits: a sample conduit. a reagent conduit and an exhaust conduit. The sample and reagent conduits would be coupled to the exhaust conduit through hundreds of smaller accurately machined capillaries. A pair of capillaries would direct the flow of sample and reagent at opposition into the exhaust path. A reaction would occur at a plurality of collision points in the exhaust.
The present invention provides a number of advantages over systems associated with the prior art. First, the light distribution is uniform across the surface. Secondly, the reaction occurs at a uniform distance from the sensing device such as a PMT. With the device of the present invention, losses under the inverse square rule are uniform and predictable. The micro-machine silicon surface is reflective. Thus, even photons emitted 180.degree. out of phase will be reflected back to sensor. Moreover, the detector material is not reactive with sample reagents. These and other objects and advantages of the present invention will become apparent from the following summary and detailed description which follows.